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author | Jim Meyering <jim@meyering.net> | 2000-08-11 09:11:20 +0000 |
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committer | Jim Meyering <jim@meyering.net> | 2000-08-11 09:11:20 +0000 |
commit | 2ed0078725f672ef530d7d2fa71300571061c2d0 (patch) | |
tree | edb5ad987a4a8020af473f25571c81141e09bc22 /doc/textutils.texi | |
parent | f64320db7bf9d4c2c84c0a50ab39314b77bb6cd1 (diff) | |
download | coreutils-2ed0078725f672ef530d7d2fa71300571061c2d0.tar.xz |
Recommend against the System V syntax
for tr ranges, and don't use it in examples. Use POSIX
classes rather than ranges, for portability.
Diffstat (limited to 'doc/textutils.texi')
-rw-r--r-- | doc/textutils.texi | 39 |
1 files changed, 21 insertions, 18 deletions
diff --git a/doc/textutils.texi b/doc/textutils.texi index 4ead6f371..b29543e09 100644 --- a/doc/textutils.texi +++ b/doc/textutils.texi @@ -3425,11 +3425,14 @@ A backslash. The notation @samp{@var{m}-@var{n}} expands to all of the characters from @var{m} through @var{n}, in ascending order. @var{m} should collate before @var{n}; if it doesn't, an error results. As an example, -@samp{0-9} is the same as @samp{0123456789}. Although GNU @code{tr} -does not support the System V syntax that uses square brackets to -enclose ranges, translations specified in that format will still work as -long as the brackets in @var{string1} correspond to identical brackets -in @var{string2}. +@samp{0-9} is the same as @samp{0123456789}. + +GNU @code{tr} does not support the System V syntax that uses square +brackets to enclose ranges. Translations specified in that format +sometimes work as expected, since the brackets are often transliterated +to themselves. However, they should be avoided because they sometimes +behave unexpectedly. For example, @samp{tr -d '[0-9]'} deletes brackets +as well as digits. Many historically common and even accepted uses of ranges are not portable. For example, on @sc{ebcdic} hosts using the @samp{A-Z} @@ -4110,7 +4113,7 @@ characters. Normally it is used for things like mapping upper case to lower case: @example -$ echo ThIs ExAmPlE HaS MIXED case! | tr '[A-Z]' '[a-z]' +$ echo ThIs ExAmPlE HaS MIXED case! | tr '[:upper:]' '[:lower:]' this example has mixed case! @end example @@ -4169,7 +4172,7 @@ The first step is to change the case of all the letters in our input file to one case. ``The'' and ``the'' are the same word when doing counting. @example -$ tr '[A-Z]' '[a-z]' < whats.gnu | ... +$ tr '[:upper:]' '[:lower:]' < whats.gnu | ... @end example The next step is to get rid of punctuation. Quoted words and unquoted words @@ -4177,7 +4180,7 @@ should be treated identically; it's easiest to just get the punctuation out of the way. @smallexample -$ tr '[A-Z]' '[a-z]' < whats.gnu | tr -cd '[A-Za-z0-9_ \012]' | ... +$ tr '[:upper:]' '[:lower:]' < whats.gnu | tr -cd '[:alnum:]_ \012' | ... @end smallexample The second @code{tr} command operates on the complement of the listed @@ -4192,8 +4195,8 @@ next step is break the data apart so that we have one word per line. This makes the counting operation much easier, as we will see shortly. @smallexample -$ tr '[A-Z]' '[a-z]' < whats.gnu | tr -cd '[A-Za-z0-9_ \012]' | -> tr -s '[ ]' '\012' | ... +$ tr '[:upper:]' '[:lower:]' < whats.gnu | tr -cd '[:alnum:]_ \012' | +> tr -s ' ' '\012' | ... @end smallexample This command turns blanks into newlines. The @samp{-s} option squeezes @@ -4206,8 +4209,8 @@ We now have data consisting of one word per line, no punctuation, all one case. We're ready to count each word: @smallexample -$ tr '[A-Z]' '[a-z]' < whats.gnu | tr -cd '[A-Za-z0-9_ \012]' | -> tr -s '[ ]' '\012' | sort | uniq -c | ... +$ tr '[:upper:]' '[:lower:]' < whats.gnu | tr -cd '[:alnum:]_ \012' | +> tr -s ' ' '\012' | sort | uniq -c | ... @end smallexample At this point, the data might look something like this: @@ -4238,8 +4241,8 @@ reverse the order of the sort The final pipeline looks like this: @smallexample -$ tr '[A-Z]' '[a-z]' < whats.gnu | tr -cd '[A-Za-z0-9_ \012]' | -> tr -s '[ ]' '\012' | sort | uniq -c | sort -nr +$ tr '[:upper:]' '[:lower:]' < whats.gnu | tr -cd '[:alnum:]_ \012' | +> tr -s ' ' '\012' | sort | uniq -c | sort -nr 156 the 60 a 58 to @@ -4265,16 +4268,16 @@ Now, how to compare our file with the dictionary? As before, we generate a sorted list of words, one per line: @smallexample -$ tr '[A-Z]' '[a-z]' < whats.gnu | tr -cd '[A-Za-z0-9_ \012]' | -> tr -s '[ ]' '\012' | sort -u | ... +$ tr '[:upper:]' '[:lower:]' < whats.gnu | tr -cd '[:alnum:]_ \012' | +> tr -s ' ' '\012' | sort -u | ... @end smallexample Now, all we need is a list of words that are @emph{not} in the dictionary. Here is where the @code{comm} command comes in. @smallexample -$ tr '[A-Z]' '[a-z]' < whats.gnu | tr -cd '[A-Za-z0-9_ \012]' | -> tr -s '[ ]' '\012' | sort -u | +$ tr '[:upper:]' '[:lower:]' < whats.gnu | tr -cd '[:alnum:]_ \012' | +> tr -s ' ' '\012' | sort -u | > comm -23 - /usr/lib/ispell/ispell.words @end smallexample |